The former model made her acting debut in Cocktail with Saif Ali Khan and Deepika Padukone.
Speaking to The Hindustan Times, she said: "They are very different, extremely different - the nature of the job and what is required from you. [Acting] is way more demanding and it has a lot more involvement - physically, emotionally and mentally."
The 27-year-old said that her lack of confidence in herself as an actor helped her win the role of the shy Indian girl Meera, who falls for Saif Ali Khan's character.
"I was from a completely different world, with no film background, I had no acting experience and no training. So I wasn't sure what I was doing there exactly. I just knew I had to meet these people (Imtiaz Ali and Homi Adajania) and I didn't know how I will tell them I am not at all prepared, but I want to meet you anyway," she explained.
"So all that hesitation, and that I was absolutely not confident about myself, came through. It so happened that they were looking for somebody like that as the character had all of that in her, so I fit the bill."
Penty began modelling in 2005 for Italian designers Trussadi and Ferre and later for Indian designers such as Rina Dhaka, Rohit Bal and Wendell Rodricks.
Penty was reportedly originally approached to star with Ranbir Kapoor in Rockstar before the role went to Nargis Fakhri.
Watch Penty in the song 'Tumhi Ho Bandhu' from Cocktail: